dGAMMA {fitODBOD} | R Documentation |
Gamma Distribution
Description
These functions provide the ability for generating probability density values, cumulative probability density values and moment about zero values for Gamma Distribution bounded between [0,1].
Usage
dGAMMA(p,c,l)
Arguments
p |
vector of probabilities. |
c |
single value for shape parameter c. |
l |
single value for shape parameter l. |
Details
The probability density function and cumulative density function of a unit bounded Gamma distribution with random variable P are given by
g_{P}(p) = \frac{ c^l p^{c-1}}{\gamma(l)} [ln(1/p)]^{l-1}
; 0 \le p \le 1
G_{P}(p) = \frac{ Ig(l,cln(1/p))}{\gamma(l)}
; 0 \le p \le 1
l,c > 0
The mean the variance are denoted by
E[P] = (\frac{c}{c+1})^l
var[P] = (\frac{c}{c+2})^l - (\frac{c}{c+1})^{2l}
The moments about zero is denoted as
E[P^r]=(\frac{c}{c+r})^l
r = 1,2,3,...
Defined as \gamma(l)
is the gamma function
Defined as Ig(l,cln(1/p))= \int_0^{cln(1/p)} t^{l-1} e^{-t}dt
is the Lower incomplete gamma function
NOTE : If input parameters are not in given domain conditions necessary error messages will be provided to go further.
Value
The output of dGAMMA
gives a list format consisting
pdf
probability density values in vector form.
mean
mean of the Gamma distribution.
var
variance of Gamma distribution.
References
Olshen AC (1938). “Transformations of the pearson type III distribution.” The Annals of Mathematical Statistics, 9(3), 176–200.
See Also
Examples
#plotting the random variables and probability values
col <- rainbow(4)
a <- c(1,2,5,10)
plot(0,0,main="Probability density graph",xlab="Random variable",ylab="Probability density values",
xlim = c(0,1),ylim = c(0,4))
for (i in 1:4)
{
lines(seq(0,1,by=0.01),dGAMMA(seq(0,1,by=0.01),a[i],a[i])$pdf,col = col[i])
}
dGAMMA(seq(0,1,by=0.01),5,6)$pdf #extracting the pdf values
dGAMMA(seq(0,1,by=0.01),5,6)$mean #extracting the mean
dGAMMA(seq(0,1,by=0.01),5,6)$var #extracting the variance
#plotting the random variables and cumulative probability values
col <- rainbow(4)
a <- c(1,2,5,10)
plot(0,0,main="Cumulative density graph",xlab="Random variable",ylab="Cumulative density values",
xlim = c(0,1),ylim = c(0,1))
for (i in 1:4)
{
lines(seq(0,1,by=0.01),pGAMMA(seq(0,1,by=0.01),a[i],a[i]),col = col[i])
}
pGAMMA(seq(0,1,by=0.01),5,6) #acquiring the cumulative probability values
mazGAMMA(1.4,5,6) #acquiring the moment about zero values
mazGAMMA(2,5,6)-mazGAMMA(1,5,6)^2 #acquiring the variance for a=5,b=6
#only the integer value of moments is taken here because moments cannot be decimal
mazGAMMA(1.9,5.5,6)